feat: make where to install the completion files configurable

Description

As a developer that does not like my system to be touched without consent from me, by any software, I love that we can disable the auto install. But it would be even better if there is an API that allows me to specify where to install. I could then hook this up on my own CLI to give my users more fine-grained control.

Requirements

• Being able to specify where to install the auto-completion files

No files, tests, or entry points are named in the issue. Start by locating the existing auto-install completion flow in the cli_completion repository, then determine how an API can accept an installation location and verify that completion files are installed there without requiring an implicit system location.